Switch Case not working with String conditions

TypeScript Version: 1.8.34

Code

// A *self-contained* demonstration of the problem follows...
let extension: String = "bin";
        switch (extension) {
            case "txt", "xml":
                return ResourceType.PlainText;
            case "bmp", "jpg", "jpeg", "png", "tiff", "psd", "tga", "gif":
                return ResourceType.Image;
            case "mp3", "wav", "ogg", "flac", "wma", "m4a":
                return ResourceType.Audio;
            case "bin", "dat":
                return ResourceType.Binary;
            case "ico":
                return ResourceType.Icon;
            case "rc", "resx":
                return ResourceType.ResourceScript;
            default:
                return ResourceType.Unknown;
}

Expected behavior:
The Switch case will return the correct value based on the condition ex when extension == "bin" ResourceType.Binary should be returned
Actual behavior:
The Default value is always returned

In JavaScript (and hence TypeScript), case clauses don't take comma-separated lists like that. But it's not an error, because a comma-separated list of expressions is a valid expression that evaluates to the result of the rightmost expression in the list. So your switch statement will only work for "xml", "gif", "m4a", "dat", "ico" and "resx" and everything else will fall through to the default case.

I think this is what you meant:

    switch (extension) {
        case "txt":
        case "xml":
            return ResourceType.PlainText;
        case "bmp":
        case "jpg":
        case "jpeg":
        case "png":
        case "tiff":
        case "psd":
        case "tga":
        case "gif":
            return ResourceType.Image;
        case "mp3":
        case "wav":
        case "ogg":
        case "flac":
        case "wma":
        case "m4a":
            return ResourceType.Audio;
        case "bin":
        case "dat":
            return ResourceType.Binary;
        case "ico":
            return ResourceType.Icon;
        case "rc":
        case "resx":
            return ResourceType.ResourceScript;
        default:
            return ResourceType.Unknown;
    }

Also, you shouldn't use String as a type (I think the team is going to try to error on that in the future) as that refers to the String global object. You should use string instead:

let extension: string = "bin";

Also, Gitter, StackOverflow or IRC are better places to ask these sort of general questions.

Addressed by comments above.

Ah thanks for letting me know

Thinking about just banning this outright. It's hard to believe anyone would ever do this on purpose

This will now be an error

(Tracking at #10814)

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Switch Case not working with String conditions #10802

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Switch Case not working with String conditions #10802

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yortus commented on Sep 9, 2016

kitsonk commented on Sep 9, 2016

RyanCavanaugh commented on Sep 9, 2016

06needhamt commented on Sep 9, 2016

RyanCavanaugh commented on Sep 9, 2016

RyanCavanaugh commented on Sep 14, 2016

RyanCavanaugh commented on Sep 14, 2016

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